1. Field of the Invention
This invention relates to an agent having a high skin depigmental effect.
2. Description of the Related Art
The mechanism of formation of spots or freckles on the skin is considered as follows: the activity of tyrosinase is promoted by the action of melanosite-irritative hormone or UV rays to have melanin eventually formed as chromatism in the skin. There is a strong demand for agents which enable acquired deposition sites, such as spots or freckles, to be restored to a normal skin color. For this purpose, a variety of agents and methods have been developed and put on the market until now. For instance, there are adopted a method wherein vitamin C (L-ascorbic acid) having good reducing ability is dosed in large amounts, a method of injecting glutathione or the like, a method using peroxides, such as hydrogen peroxide, zinc peroxide, sodium peroxide and the like, which are believed to have the bleaching action of melamine, and a method wherein vitamin C or cysteine is applied to local sites in the form of an ointment, cream, lotion or the like. In Europe and America, a hydroquinone agent has been used as a medicine [A.B. Lerner and Fitzpatrick, Biochemistry of Melanin Formation, 30, 91(1950)].
Vitamin C has a problem with respect to stability and becomes so unstable in water-containing systems that they will cause changes in odor and color. Thiol compounds such as glutathione and cysteine do not exhibit a satisfactory depigmental effect since the development of the effect is very slow.